Pigment for paper and coatings

ABSTRACT

Provided is a kaolin having a finer particle size and a narrower particle size distribution, in combination with suitable morphology. Also provided are a method of preparing the kaolin product and methods of use.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 62/305,252, filed on Mar. 8, 2016, and U.S. Provisional ApplicationSer. No. 62/449,298, filed on Jan. 23, 2017, the disclosures of whichare incorporated herein by reference in their entireties.

FIELD OF THE DISCLOSURE

The present application relates to pigments for paper coatings,particularly to heat-treated kaolin pigments.

BACKGROUND OF THE DISCLOSURE

In the discussion of the background that follows, reference is made tocertain structures and/or methods. However, the following referencesshould not be construed as an admission that these structures and/ormethods constitute prior art. Applicants expressly reserve the right todemonstrate that such structures and/or methods do not qualify as priorart.

Kaolin is a naturally-occurring hydrated aluminum silicate crystallinemineral (kaolinite), in the form of hexagonally shaped, stackedplatelets of irregular orientation. Hydrous kaolin is characterized byits fine particle size, plate like or lamellar particle shape, andchemical inertness.

Current methods of producing calcined kaolin involve preparing achemically dispersed blunged/degritted kaolin crude, subjecting it tocentrifugation and magnetic separation, followed by spray drying,pulverization, calcination and pulverization. Current techniques forobtaining finer particle size kaolin, such as media grinding, have adetrimental effect on the morphology of the calcined kaolin and anegative impact on performance in the final application of the kaolinproduct.

Calcination of kaolin at temperatures up to about 1100° C. cementsparticles together and produces products of improved whiteness andopacity. Such pigments are widely used by the paper, plastics, rubberand paint industries. U.S. Pat. No. 3,586,523 to Fanselow et al, isdirected to producing low abrasion fine particle size opacifyingcalcined kaolin clay, such as the pigments supplied under the registeredtrademarks ANSILEX® and ANSILEX® 93. Such pigments have an averageparticle size of about 0.8 microns.

There is an on-going unmet need in the art for a heat-treated kaolinproduct with both a finer and steeper particle size distribution anduseful performance properties and methods of producing same in order toimprove performance in various applications. The present disclosureaddresses this need.

SUMMARY OF THE DISCLOSURE

The following summary is not an extensive overview. It is intended toneither identify key or critical elements of the various embodiments,nor delineate their scope.

Provided is a heat-treated kaolin having a GE brightness of at leastabout 92 and a particle size distribution of: equal to or greater than99% of particles with an equivalent spherical diameter (e.s.d.) of lessthan 10 microns; equal to or greater than 93% of particles with ane.s.d. of less than 5 microns; equal to or greater than 85% of particleswith an e.s.d. of less than 2 microns; equal to or greater than 77% ofparticles with an e.s.d. of less than 1 microns; and equal to or greaterthan 25% of particles with an e.s.d. of less than 0.5 micron, whereinthe percentages (%) are based on the total weight of the particles inthe heat-treated kaolin. The heat-treated kaolin can have a particlesize distribution of: 99% to 100% of particles with an e.s.d. of lessthan 10 microns; 93% to 100% of particles with an e.s.d. of less than 5microns; 85% to 98% of particles with an e.s.d. of less than 2 microns;77% to 92% of particles with an e.s.d. of less than 1 microns; and 25%to 46% of particles with an e.s.d. of less than 0.5 micron, wherein thepercentages (%) are based on the total weight of the particles in theheat-treated kaolin n. In some embodiments, the heat treated kaolin canhave a +325 mesh residue content of 300 ppm or less. For example, theheat treated kaolin can have a +325 mesh residue content of from 5 ppmto 300 ppm (such as 90 ppm or less, 70 ppm or less, or 50 ppm or less).In some embodiments, the heat-treated kaolin can have a sodium oxidecontent of less than or equal to 0.25% by weight (such as less than orequal to 0.1% by weight). The titania content of the heat-treated kaolincan be less than or equal to 1.5% by weight.

The heat-treated kaolin can have a GE brightness of at least about 92 toabout 96.

The heat-treated kaolin can have median particle size (d50) equal to orless than about 0.65 micron. The heat-treated kaolin can have a medianparticle size (d50) of 0.50 to 0.65 micron.

The heat-treated kaolin can have an oil absorption of equal to orgreater than 100 pounds of oil per 100 pounds of clay (i.e.,heat-treated kaolin) (lbs oil/100 lbs heat-treated kaolin). Theheat-treated kaolin can have an oil absorption of from greater than 100to 140 lbs oil/100 lbs heat-treated kaolin (such as from greater than100 to 130 lbs, from 105 to 120 lbs, or from 105 to 115 lbs oil/100 lbsheat-treated kaolin).

The heat-treated kaolin can have a scattering coefficient at 457nanometers of equal to or greater than 0.300 m²/g. The heat-treatedkaolin can have a scattering coefficient at 457 nanometers of about0.305 to about 0.335 m²/g.

The heat-treated kaolin can have a scattering coefficient at 577nanometers of equal to or greater than 0.220 m²/g. The heat-treatedkaolin can have a scattering coefficient at 577 nanometers of about0.223 to about 0.230 m²/g.

The heat-treated kaolin can have a surface area of equal or greater than17.0 m²/g. For example, the heat-treated kaolin can have a surface areaof about 17.0 to about 25.0 m²/g, from about 17.0 to about 21.0 m²/g, orgreater than 20.0 m²/g.

The heat-treated kaolin can have an Einlehner abrasion loss equal to orless than 18 mg/10⁵ rev. The heat-treated kaolin can have an Einlehnerabrasion loss of 9 to 18 mg/10⁵ rev.

The heat-treated kaolin can have a gloss of equal to or greater than30%. The heat-treated kaolin can have a gloss of about 30% to about 45%.

The heat-treated kaolin can be fully calcined or can be metakaolin.

Also provided is an article of manufacture comprising the heat-treatedkaolin of the disclosure. The article can be selected from the groupconsisting of: a paper product, a paperboard product, a paper coatingcomposition, a ceramic composition, a paint composition, a polymercomposition, a rubber composition, an engineered plastic composition,and an ink composition.

The article of manufacture can be a paper product. The article ofmanufacture can be a thermal paper. The article of manufacture can be athermal paper having a base layer that comprises the kaolin.

The article of manufacture can be a paint composition.

Also provided is a method for preparing the heat-treated kaolin productof the disclosure. The method comprises the steps of: providing a firstkaolin feedstream having at least about 88-89% by weight of theparticles having size of 1 μm or less; classifying the first kaolinfeedstream by centrifugation to provide a fine particle sizedistribution of at least about 97-98% by weight of the particles havingsize of 1 μm or less; filtering the first kaolin feedstream to produce afilter cake; dispersing the filtrate in a sodium-free dispersion agentto provide a second kaolin feedstream; and drying and heat treating thesecond kaolin feedstream, wherein the method for preparing theheat-treated kaolin does not include a reductive bleaching step. Thesodium-free dispersion agent can be an ammonia-based dispersion agent.The second kaolin feedstream can have a pH of about 10.

The method can further comprise flocculating the first feedstream priorto the filtering step.

The heat treating step of the method can comprise calcining at atemperature of from about 900° C. to about 1200° C. to produce a fullycalcined kaolin.

The providing step of the method can comprise processing ablunged/degritted hydrous kaolin crude feedstock by a classificationstep and a beneficiation step to produce the first kaolin feedstreamhaving at least about 88-89% by weight of the particles having size of 1μm or less. The beneficiation step of the processing step comprisesmagnetic separation. In certain embodiments, the processing step canfurther comprise a flotation step and the first kaolin feedstream has atleast about 70% by weight of the particles having size of 0.3 μm orless. In some examples, the method can include an ozonation stepsubsequent to the flotation step. In other embodiments, the processingstep can further comprise a selective flocculation step and the firstkaolin feedstream has at least about 86% by weight of the particleshaving size of 0.5 μm or less.

The method can exclude delamination processes. Excluded delaminationprocesses can include ball milling, stirred media grinding, and/or highenergy media grinding.

The method can be carried out wherein the classifying step, filteringstep, dispersing step, and drying and calcining step exclude asodium-based dispersion agent.

As envisioned in the present disclosure with respect to the disclosedmethods and compositions of matter, in one aspect the embodiments of thedisclosure comprise the components and/or steps disclosed therein. Inanother aspect, the embodiments of the disclosure consist essentially ofthe components and/or steps disclosed therein. In yet another aspect,the embodiments of the disclosure consist of the components and/or stepsdisclosed therein.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the various products, compositions andmethods, there are depicted in the drawings certain embodiments.However, the products, compositions, methods of making them, and methodsof their use are not limited to the precise arrangements andinstrumentalities of the embodiments depicted in the drawings.

FIG. 1 is a schematic representation of the method of preparing thekaolin of the disclosure.

FIG. 2 is a schematic representation of an embodiment of the method ofpreparing the kaolin of the disclosure.

FIG. 3 is a schematic representation of an embodiment of the method ofpreparing the kaolin of the disclosure.

FIG. 4 depicts particle size distribution data (obtained using aSedigraph 5100 particle size analyzer) in graph form for Samples 1-3according to the present disclosure and Comparative Sample 1.

DETAILED DESCRIPTION

There is a need in the art for a kaolin product, such as a partially orfully calcined kaolin, with finer and steeper particle sizedistribution, while possessing appropriate morphology for desiredproperties. Provided herein is a heat treated kaolin product with finerand narrower particle size distribution compared to current calcinedkaolin products. In an embodiment, the kaolin product is fully calcined.The heat-treated kaolin of the present disclosure has an appropriatemorphology to provide desired performance that is comparable to orbetter than current commercially available calcined kaolin products. Forinstance, the heat-treated kaolin does not have a loss of lightscattering coefficient and/or reduced opacity, yet a finer and steeperparticle size distribution is achieved. The kaolin of the presentdisclosure may have an increased light scattering coefficient, increasedoil absorption, and/or increased surface area, compared to currentcommercially available calcined kaolin products. A method of producingthe disclosed kaolin is provided. The method includes the use of adispersant that is free of alkali and alkaline earth metals, and inparticular, free of sodium. Products comprising the kaolin of thepresent disclosure and methods of use of the kaolin are also provided.

Definitions

As used herein, each of the following terms has the meaning associatedwith it in this section.

The articles “a” and “an” are used herein to refer to one or to morethan one (i.e., to at least one) of the grammatical object of thearticle. By way of example, “an element” means one element or more thanone element.

The term “about” will be understood by persons of ordinary skill in theart and will vary to some extent depending on the context in which it isused. As used herein, “about” is meant to encompass variations of ±20%,more preferably ±10%, more preferably ±5%, even more preferably ±1%, andstill more preferably ±0.1%.

It is understood that any and all whole or partial integers between anyranges set forth herein are included herein.

Compositions

Provided herein is an improved kaolin, a method of preparing theimproved kaolin, and products and compositions comprising the improvedcalcined kaolin.

The heat-treated kaolin of the disclosure has improved morphology andperformance, compared to standard commercial calcined kaolin products.The morphology of the calcined kaolin includes being irregular in shapeand having increased void volume. The inventive calcined kaolin pigmenthas one or more improved properties, such as finer particle sizedistribution, finer median particle size, increased surface area,increased brightness, reduced abrasion loss, improved oil absorption,lower residue content, lower sodium oxide content, and comparable orincreased scattering coefficient. Notably, the oil absorption of thecalcined kaolin product of the disclosure is unexpectedly increased, ascompared to current commercial products with similar particle size.Moreover, the kaolin product of the disclosure has a finer particle sizedistribution, while still achieving the correct morphology to provide,for instance, highly desirable scattering properties. The improvedkaolin results from the hydrous kaolin processing method disclosedherein. The processing method includes utilizing a finer particle sizekaolin feedstream for calcination and not using a dispersant comprisingan alkali metal such as sodium. The method in an embodiment uses insteadusing an ammonia-based dispersant as the filter dispersant prior tocalcination to prepare the improved calcined kaolin product. In somecases, the processing method does not utilize bleach, which may resultin coarser particles and alter properties such as residue content and/orparticle size of the calcined kaolin product.

Particle size distribution (PSD) as used herein is determined with theSEDIGRAPH 5100 particle size analyzer (Micromeretics Corporation) on acalcined kaolin in a fully dispersed condition in a standard aqueousmedium, such as water. The data are reported as equivalent sphericaldiameters (e.s.d.) on a weight percentage basis. The median particlesize d50 is the value determined in this way of the particle e.s.d. atwhich there are 50% by weight of the particles that have an e.s.d. lessthan the d50 value.

The calcined kaolin of the disclosure has a narrower particle sizedistribution and finer median particle size.

The calcined kaolin can have a median particle size (d50) of about 0.65micron or less. For example, the calcined kaolin can have a medianparticle size of 0.60 micron or less, 0.59 micron or less, 0.58 micronor less, 0.57 micron or less, 0.56 micron or less, 0.55 micron or less,0.54 micron or less, or 0.53 micron or less. In some embodiments, thecalcined kaolin can have a median particle size of 0.50 micron orgreater, 0.51 micron or greater, 0.52 micron or greater, 0.53 micron orgreater, 0.54 micron or greater, or 0.55 micron or greater. In someembodiments, the calcined kaolin can have a median particle size of from0.50 to 0.65 micron, 0.50 to less than 0.60 micron, 0.50 to 0.59 micron,0.50 0.58 micron, 0.50 to 0.57 micron, or 0.52 to 0.58 micron.

Representative ranges for PSD and mean particle size for the calcinedkaolin of the disclosure are provided in Table 1. PSD and mean particlesize for representative calcined kaolins are provided in Table 2.

TABLE 1 Ranges  % ≦10 μm ≧99  99-100   % ≦5 μm ≧93  93-100 94-98 96-97  % ≦2 μm ≧85 85-98 89-95 89-93   % ≦1 μm ≧77 77-92 77-90 77-86 % ≦0.5μm ≧25 25-46 27-40 28-39 % ≦0.3 μm ≧4  4-10 4-9 4-7 % ≦0.2 μm ≧0 0-6 0-53-5 d50 (μm) ≦0.65 0.50-0.65 0.52-0.63 0.55-0.63

TABLE 2 Representative kaolins A B C D E  % ≦10 μm 100 100 99 100 100  % ≦5 μm 96 97 94 97 97   % ≦2 μm 91 90 89 93 93   % ≦1 μm 86 77 82 8787 % ≦0.5 μm 37 29 33 32 32 % ≦0.3 μm 7 4 7 6 7 % ≦0.2 μm 5 0 3 3 3 d50(μm) 0.57 0.63 0.59 0.59 0.59

The calcined kaolin of the disclosure has one or more of improvedbrightness, reduced abrasion loss, improved oil adsorption and increasedsurface area.

As used herein, brightness is determined by the TAPPI standard methodT452. The data are reported as the percentage reflectance to light of a457 nm wavelength (GEB value).

The calcined kaolin can have a brightness of 92% or greater. Forexample, the calcined kaolin can have a brightness of 93% or greater,94% or greater, 95% or greater, 96% or greater, or 97% or greater. Insome embodiments, the calcined kaolin can have a brightness of from 92%to 97% or from 92% to 96%.

Kaolin deposits usually contain titania minerals. The titania mineralscan be present as polymorphs having the composition TiO₂. Naturaltitania exhibits low brightness, the presence of which can decreasekaolin brightness. The calcined kaolin can have a titania content of1.5% by weight or less. For example, the calcined kaolin can have atitania content of 1.45% or less, 1.3% or less, 1.2% or less, 1.0% orless, 0.9% or less, 0.8% or less, 0.7% or less, 0.6% or less, or 0.5% orless by weight, based on the total weight of the calcined kaolin. Insome embodiments, the calcined kaolin can have a titania content of 0%or greater, 0.5% or greater, or 1% or greater by weight, based on thetotal weight of the calcined kaolin. In some embodiments, the calcinedkaolin can have a titania content of from 0% to 1.45%, from 0.5% to1.45%, or from 0.5% to 1.2% by weight, based on the total weight of thecalcined kaolin.

As used herein, Einlehner abrasion loss is determined by an Einlehner AT1000 Abrasion tester, using 15 weight % solids and 100,000 revolutions.The Einlehner abrasion is reported in mg loss/100,000 revolutions (mgloss/10⁵ rev).

The calcined kaolin can have an Einlehner abrasion loss of 18 mg/10⁵ revor less. For example, the calcined kaolin can have an Einlehner abrasionloss of 15 mg/10⁵ rev or less, 12 mg/10⁵ rev or less, 10 mg/10⁵ rev orless, or 9 mg/10⁵ rev or less. In some embodiments, the calcined kaolincan have an Einlehner abrasion loss of 5 mg/10⁵ rev or greater or 9mg/10⁵ rev or greater. In some embodiments, the calcined kaolin can havean Einlehner abrasion loss of from 9 to 18 mg/10⁵ rev, from 9 to 16mg/10⁵ rev, or from 9 to 15 mg/10⁵ rev.

As used herein, oil absorption is determined using ASTM D 281 “OilAbsorption by Spatula Rub-out.” The data are reported in pounds (grams)of oil absorbed per 100 pounds (grams) of calcined kaolin (%).

The calcined kaolin can have an oil absorption of 100% or greater (100lbs or greater oil per 100 lbs calcined (heat treated) kaolin). Forexample, the calcined kaolin can have an oil absorption of greater than100%, 105% or greater, 110% or greater, 115% or greater, 120% orgreater, 125% or greater, 130% or greater, or 135% or greater. In someembodiments, the calcined kaolin can have an oil absorption of from 100%to 115%, from 100% to 130%, from greater than 100% to 115%, from greater100% to 130%, from greater 100% to 140%, from 105% to 120%, from 105% to130%, from 105% to 140%, from 109% to 130%, or from 109% to 120%.

As used herein, surface area is determined by the art-recognizedBrunaruer Emmett Teller (BET) method using N₂ as the adsorbate. Inbrief, the surface area of a calcined kaolin sample, frozen in liquidnitrogen, is measured by adsorption of nitrogen gas and quantifiedthrough BET analysis.

The calcined kaolin can have a surface area of 17 m²/g or greater. Forexample, the calcined kaolin can have a surface area of greater than 17m²/g, 18 m²/g or greater, 19 m²/g or greater, 20 m²/g or greater, 21m²/g or greater, or 22 m²/g or greater. In some embodiments, thecalcined kaolin can have a surface area of 25 m²/g or less, 24 m²/g orless, 23 m²/g or less, or 22 m²/g or less. In some embodiments, thecalcined kaolin can have a surface area of from 17 m²/g to 25 m²/g, from17 m²/g to 22 m²/g, from 19 m²/g to 25 m²/g, from greater than 20 m²/gto 25 m²/g, or from 21 m²/g to 25 m²/g.

Representative ranges for brightness, abrasion loss, oil absorption andsurface area for the calcined kaolin of the disclosure are provided inTable 3. Brightness, abrasion loss, oil absorption and surface areavalues for representative calcined kaolins are provided in Table 4.

TABLE 3 Property Ranges G.E. Brightness, % ≧92 92-97 92-96 92-95Einlehner Abrasion ≦18  9-18 10-16 10-15 loss in mg/10⁵ rev OilAbsorption, % ≧100 100-115 105-115 106-113 Surface Area (m²/g) ≧17.017.0-23   17.5-22   17.5-21  

TABLE 4 Representative kaolins Property A B C D E G.E. Brightness, %92.3 92.4 94.3 93.2 92.9 Einlehner Abrasion 18.1 nd 10.1 14.4 nd loss inmg/10⁵ rev Oil Absorption, % 89 109 113 110 110 Surface Area (m²/g) 16.917.8 20.8 19.6 19.7 “nd” = not determined

The calcined kaolin of the disclosure has improved gloss and/or lightscattering.

As used herein, gloss is determined by applying a film of pigment ontooptically smooth black glass from a 30% solids (by weight) mixture ofpigment and water using a 0.25 mil Bird Bar. Gloss is measured using aTechnidyne T480 gloss meter (Technidyne Corporation, New Albany, Ind.)at 75 degrees (PL Method 50C).

The calcined kaolin can have a gloss of 30% or greater. For example, thecalcined kaolin can have a gloss of 32% or greater, 35% or greater, 38%or greater, 40% or greater, 42% or greater, 44% or greater, 45% orgreater, 46% or greater, 48% or greater, or 50% or greater. In someembodiments, the calcined kaolin can have a gloss of 50% or less, 48% orless, 47% or less, or 46% or less. In some embodiments, the calcinedkaolin can have a gloss of from 30% to 50%, from 30% to 45%, from 35% to50%, or from 35% to 45%.

As used herein, light scattering is determined by applying a film ofpigment onto optically smooth black glass from a 30% solids (by weight)mixture of pigment and water using a 0.25 mil Bird Bar. The reflectancevalues of the pigment films after air drying are measured at wavelengthsof 457 nm and 577 nm by means of a reflectance meter having anintegrated sphere geometry like an Elrepho reflectometer. Thereflectance values are converted by the use of Kubelka-Munk equations tolight scattering coefficients (m²/g).

The calcined kaolin can have a scattering coefficient at 457 nanometersof 0.400 m²/g or less. For example, the calcined kaolin can have ascattering coefficient at 457 nanometers of 0.380 m²/g or less, 0.350m²/g or less, 0.340 m²/g or less, 0.335 m²/g or less, 0.330 m²/g orless, 0.325 m²/g or less, 0.320 m²/g or less, 0.315 m²/g or less, 0.310m²/g or less, 0.305 m²/g or less, or 0.300 m²/g or less. In someembodiments, the calcined kaolin can have a scattering coefficient at457 nanometers of greater than 0.300 m²/g, 0.305 m²/g or greater, 0.310m²/g or greater, or 0.320 m²/g or greater. In some embodiments, thecalcined kaolin can have a scattering coefficient at 457 nanometers offrom 0.300 m²/g to 0.400 m²/g, from 0.300 m²/g to 0.350 m²/g, from 0.300m²/g to 0.335 m²/g, or from 0.305 m²/g to 0.335 m²/g.

The calcined kaolin can have a scattering coefficient at 577 nanometersof 0.300 m²/g or less. For example, the calcined kaolin can have ascattering coefficient 577 nanometers of 0.250 m²/g or less, 0.235 m²/gor less, 0.229 m²/g or less, 0.228 m²/g or less, 0.227 m²/g or less,0.226 m²/g or less, 0.225 m²/g or less, 0.224 m²/g or less, 0.223 m²/gor less, 0.222 m²/g or less, 0.221 m²/g or less, or 0.220 m²/g or less.In some embodiments, the calcined kaolin can have a scatteringcoefficient at 577 nanometers of greater than 0.220 m²/g, 0.221 m²/g orgreater, 0.222 m²/g or greater, 0.223 m²/g or greater, 0.224 m²/g orgreater, or 0.225 m²/g or greater. In some embodiments, the calcinedkaolin can have a scattering coefficient at 577 nanometers of from 0.220m²/g to 0.300 m²/g, from 0.221 m²/g to 0.229 m²/g, or from 0.221 m²/g to0.227 m²/g.

Representative ranges for gloss and light scattering coefficient for thecalcined kaolin of the disclosure are provided in Table 5. Gloss andlight scattering coefficient values for representative calcined kaolinsare provided in Table 6.

TABLE 5 Property Ranges Gloss, % ≧30 30-45 35-45 36-44 S₄₅₇ (m²/g)≧0.300 0.300-0.400 0.305-0.335 0.309-0.331 S₅₇₇ (m²/g) ≧0.2200.220-0.300 0.223-0.230 0.225-0.229

TABLE 6 Representative kaolins Property A B C Gloss, % 43.3 36.6 31.0S₄₅₇ (m²/g) 0.331 0.309 0.327 S₅₇₇ (m²/g) 0.229 0.225 0.227

Calcined kaolin products can include a small percentage of oversizeparticles (coarse residue particles) that can have undesirable effectssuch as blockage of the die in extrusion processes. These coarse residueparticles can also cause deficiencies on the coated paper/thermal papersurface. Further, the coarse residue particles tend to be more abrasiveand can therefore result in wear and tear of application equipment. Thecoarse residue particles will generally be retained on a 325 mesh screenand are referred to herein as +325 mesh residue. The +325 mesh residuemay be measured as specified in ASTM C-325-81 (1997).

The calcined kaolin can have a +325 mesh residue content of 300 ppm orless. For example, the calcined kaolin can have a +325 mesh residuecontent of 280 ppm or less, 250 ppm or less, 230 ppm or less, 200 ppm orless, 180 ppm or less, 150 ppm or less, 120 ppm or less, 100 ppm orless, less than 100 ppm, 95 ppm or less, 90 ppm or less, 80 ppm or less,70 ppm or less, 60 ppm or less, 50 ppm or less, 40 ppm or less, 30 ppmor less, 25 ppm or less, or 20 ppm or less. In some embodiments, thecalcined kaolin can have a +325 mesh residue content of 0 ppm orgreater, 5 ppm or greater, 10 ppm or greater, 15 ppm or greater, 20 ppmor greater, 30 ppm or greater, 40 ppm or greater, 50 ppm or greater, 55ppm or greater, 60 ppm or greater, 65 ppm or greater, or 70 ppm orgreater. In some embodiments, the calcined kaolin can have a +325 meshresidue content of from 5 ppm to 300 ppm, from 5 ppm to 250 ppm, from 5ppm to 200 ppm, from 5 ppm to 150 ppm, from 5 ppm to 100 ppm, from 10ppm to 300 ppm, from 10 ppm to 200 ppm, from 10 ppm to 100 ppm, from 10ppm to 80 ppm, from 15 ppm to 300 ppm, from 15 ppm to 200 ppm, from 15ppm to 100 ppm, or from 15 ppm to 75 ppm.

Calcined kaolin products can include a low alkali content, includingsodium oxide and potassium oxide. Sodium oxide and potassium oxide areknown to have high thermal expansion values and are thus undesirable insome applications. The calcined kaolin can have an alkali content of0.25% by weight or less, based on the total weight of the calcinedkaolin. In some embodiments, the calcined kaolin can have a sodium oxidecontent of 0.20% by weight or less, 0.18% by weight or less, 0.15% byweight or less, 0.13% by weight or less, 0.10% by weight or less, 0.08%by weight or less, or 0.05% by weight or less, based on the total weightof the calcined kaolin. In some embodiments, the calcined kaolin canhave a sodium oxide content of from 0.05% to 0.20% by weight, 0.05% to0.15% by weight, or from 0.05% to 0.10% by weight, based on the totalweight of the calcined kaolin.

The heat-treated kaolin of the disclosure can comprise any combinationof the herein described properties. Thus, the disclosure encompasses aheat-treated kaolin having a PSD as disclosed in Table 1 in combinationwith a median particle size as disclosed in Table 1 and/or any one ormore of the properties disclosed in Tables 3 and 5. The disclosureencompasses a heat-treated kaolin having a PSD as disclosed in Table 1and having the light scattering values disclosed in Table 5. Thedisclosure encompasses a heat-treated kaolin having a PSD as disclosedin Table 1 and having the oil absorption values disclosed in Table 3.

A method for preparing the kaolin product is provided. The method isdepicted in schematic form in FIG. 1. The method comprises providing afirst kaolin feedstream 6 having at least about 88-89% by weight of theparticles of size of 1 μm or less; a filtering step 8 of the firstfeedstream to produce a filter cake 10; a dispersing step 12 of thefilter cake in a sodium-free dispersion agent to provide a second kaolinfeedstream 14; and a drying and heat treating step 16 of the secondkaolin feedstream to produce a heat treated kaolin 18.

An embodiment of the method is depicted in schematic form in FIG. 2 inwhich prior to filtering step 8, the first kaolin feedstream is subjectto a step of classifying 20 to produce a finer particle size feedstreamhaving at least 97-98% by weight of particles have size of 1 μm or less.The finer particle size feedstream is subject to a step of flocculating22, followed by filtering step 8 to produce filter cake 10. Filter cake10 is subject to the dispersing step 12 to provide second kaolinfeedstream 14. Drying and heating step 16 comprises a step of firstspray drying 24 the second kaolin feedstream 14 and then subjectingfeedstream 14 to a step of pulverizing 26, followed by a step heattreating 28 the pulverized kaolin material to produce heat treatedkaolin 18. Optionally, heat treated kaolin 18 is subject to further stepof pulverizing 30 to produce a pulverized heat treated kaolin 32.

The method may further comprise producing the first kaolin feedstream 6by a processing step 4 comprising processing a blunged/degritted hydrouskaolin crude feedstock 2 by a classification step and a beneficiationstep to produce the first kaolin feedstream 6. See FIG. 3.

The blunged/degritted hydrous kaolin crude feedstock can be preparedfrom a kaolin crude using conventional techniques. Any hydrous kaolincrude can be used. Kaolin crudes can be pre-dominantly grey, white,creamy, pink or red/brown in color so the present disclosure providesversatility of using a wide variety of crudes to obtain the finalcalcined kaolin product.

Typically, the kaolin crude is crushed and made down into a slurry form(blunged in water) with the aid of one or more anionic dispersantsthrough the use of a high-energy mixer known as a blunger. After thisblunging step, the pH of the dispersed slurry is usually about 7 to 10.In some embodiments, the slurry has a pH of about 10 (e.g., 9 to 10 or9.5 to 10). The dispersant may be an organic dispersant or inorganicdispersant. Inorganic dispersant typically include phosphate salts andsodium silicate dispersants. Examples of phosphate salts includeinorganic polyphosphates and pyrophosphates (which are actually a typeof polyphosphate), such as sodium hexametaphosphate (SHMP), sodiumtripolyphosphate (STPP) and tetrasodium pyrophosphate (TSPP). Organicdispersants typically include ammonia-based dispersants, sulfonatedispersants, carboxylic acid dispersants, and polymeric dispersants,such as polyacrylate dispersants, as well as other organic dispersantsconventionally employed in kaolin pigment processing. Dispersant blendsmay be used, such as a blend of sodium carbonate, sodium polyacrylate,sodium silicate, and sodium hydroxide, as disclosed in U.S. Pat. No.8,664,319.

Oversized particles (grit) consisting largely of sand particles are thenremoved from the blunged crude by any conventional manner using one ormore of sieves, sandboxes, gravity settling, or hydrocyclones. Eitherwet or dry degritting may be employed. For example, degritting may beperformed by combining the crude kaolin with water and passing theslurried mixture through a sieve, such as a 325 mesh sieve or a 200 meshsieve.

The resulting blunged/degritted hydrous kaolin crude feedstock is thenprocessed by a classification step and a beneficiation step to produce afirst feedstream.

Classification (also known as fractionation) and beneficiation (alsoknown as refining) may be accomplished using any known methods. Methodsof classification include centrifugation and sedimentation. Appropriatemethods include gravity sedimentation or elutriation, any type ofhydrocyclone apparatus, or, centrifugation. Examples of suitablecentrifuges include Bird solid bowl centrifuge, disc-nozzle high speedcentrifuges, horizontal three-phase centrifuges, and the like.High-speed centrifugation serves to separate the blunged/degritted crudekaolin into two streams. In a non-limiting example, centrifugationseparates the kaolin into a coarse stream (at least about 80% by weightof the particles have a size of 2 microns or coarser) and a fine stream(at least about 85% by weight of the particles have a size of 1 micronor less). In an embodiment, centrifugation is such that the firstfeedstream, after beneficiation, has at least about 88-89% by weight ofthe particles have size of 1 μm or less.

Methods of beneficiation include magnetic separation, selectiveflocculation, reductive bleaching, filtering, flotation, andozonation/oxidative bleaching. The methods may be carried out in anysuitable manner. In an embodiment, the beneficiation step is magneticseparation. In an embodiment, the beneficiation is ozonation/oxidativebleaching.

Magnetic separation can be effected using a high gradient magneticseparator (HGMS), to magnetically remove colored discrete paramagneticimpurities (principally iron-bearing titania), thus improvingbrightness. These separators are also known as HIMS units (highintensity magnetic separators). Conventional or improved HGMS separatorscan be employed for the magnetic separation step. Suitable magneticseparators include any commercial or proprietary “high intensity”magnetic separator.

Flocculation involves separating minerals of one species from mineralsof the same species, e.g., the separation of ultrafine kaolin particlesfrom fine or coarse kaolin particles. Flocculation is effected using anionic material, such as an acid (“acid flocculation”). Sulfuric acid isan inexpensive and widely available acid. Flocculation may be carried inany suitable manner.

Selective flocculation involves separation of ultrafine kaolin particlesfrom discolored titania-ferrous impurities by the aid of conditioningchemicals (such as oleic acid and divalent cation salts) and highmolecular weight/highly anionic acrylamide polymer in a settling vesselsuch as classifier or thickener. Methods of separating kaolin particlesfrom titania-ferrous impurities using selective flocculation techniqueare described in U.S. Pat. No. 5,535,890.

Flotation is performed in any conventional manner including wetflotation, ultraflotation, froth flotation, TREP flotation (titaniaremoval and extraction process), and the like. General methods offlotation are described in Mathur, S., “Kaolin Flotation”, Journal ofColloid and Interface Science, 256, pp. 153-158, 2002, which is herebyincorporated by reference in this regard. See also U.S. Pat. No.8,557,037.

Generally, bleaching involves increasing the brightness of the kaolin.Reductive bleaching involves contacting the coarse kaolin stream with asuitable amount of one or more of hydrosulfite (dithionite) salts,potassium permanganate, alkali bichromates, ammonium persulfate, and thelike. See, e.g., U.S. Pat. No. 3,353,668. In some embodiments, themethod for preparing the kaolin product does not include reductivebleaching. Thus, the kaolin stream can be free or substantially free ofsoluble salts from the bleaching process. The presence of soluble saltssuch as potassium permanganate and zinc hydrosulfite can affect thekaolin product. For example, a high concentration of soluble salts cancause a higher +325 mesh residue content, coarser particle size, orundesirably large increases in oil absorption. The presence of solublesalts can also flocculate the kaolin which may affect processing thekaolin. For example, a high concentration of soluble salts can causehigh viscosity of the kaolin product in paper use, or lower thetemperature of vitrification in ceramic utilization.

Ozonation/oxidative bleaching involves oxidative bleaching, using ozone,in order to bleach components, such as organic discolorants, that may bepresent. The ozone acts not only to destroy substantial portions ofdiscoloring organics, but also destroys by oxidation the organicdispersant, if such a compound is present. However, the ozone does notdestroy inorganic dispersants. Ozonation is performed in any suitablemanner. In a non-limiting example, ozonation may be performed at adosage level from about 0.1 to about 20 pounds of ozone per ton ofkaolin. In another embodiment, ozonation is performed at a dosage levelfrom about 0.5 to about 10 pounds of ozone per ton of kaolin. The ozonemay be applied as a stream of bubbles which can be passed upwardlythrough the slurry. This can be a batch process or a continuous processin which the ozone bubbles pass counter current to a flow of the slurryin a pipe or other conduit, such as mixed and packed column.

After the blunged/degritted hydrous kaolin crude feedstock is processedby a classification step and a beneficiation step, the result is a firstfeedstream having at least about 88-89% by weight of the particles havesize of 1 μm or less.

Optionally, the blunged/degritted hydrous kaolin crude feedstock issubject to two classification steps, e.g., a coarse size classification,and finer size classification. In an embodiment in which the feedstockis subject to two classification steps, the first feedstream produceshas at least 70% by weight of the particles have size of <0.3 microns.In an embodiment in which the feedstock is subject to two classificationsteps, the first feedstream produces has at least 86% by weight of theparticles have size of <0.5 microns.

Optionally, the method includes a further beneficiation step on theblunged/degritted hydrous kaolin crude feedstock. In an embodiment, theblunged/degritted hydrous kaolin crude feedstock is subject to ozonationand flotation beneficiation steps. In an embodiment, theblunged/degritted hydrous kaolin crude feedstock is subject to magneticseparation and acid flocculation beneficiation steps.

The first feedstream is then subjected to a second beneficiation step offiltering to produce a filter cake. Filtering serves to removesolubilized impurities along with by-products salts by dewatering,typically following by rinsing with clean water.

In an embodiment, the method further comprises a second classificationstep prior to the filtering step. Specifically, the first feedstream isclassified by centrifugation to provide a fines fraction having a fineparticle size distribution of at least about 97-98% by weight of theparticles have size of 1 μm or less. The fines fraction of the firstfeedstream is then filtered to produce a filter cake product. The finefraction optionally may be flocculated prior to filtration. See FIG. 2.

Centrifugation can be done in a single or multiple steps by using solidbowl or disc nozzle centrifuges to provide the desired particlefineness. In a high-speed centrifugation treatment the centrifuge mayoperate at “g” forces from above about 1,000 to about 10,000. In anotherembodiment, the high-speed centrifugation treatment the centrifuge mayoperate at “g” forces from about 2,000 to about 7,500. In yet anotherembodiment, the high-speed centrifugation treatment the centrifuge mayoperate at “g” forces from above about 2,500 to about 5,000.

The filter cake produced by the filtering step is then dispersed in asodium-free dispersion agent to provide a second feedstream. Exemplarysodium-free dispersants include ammonia-based dispersants. Exemplaryammonia-based dispersants include ammonia, ammonium polyacrylate,ammonium polyphosphate, AMP-95 (2-amino-2-methyl-1-propanol) orcombination thereof.

The second feedstream is then dried and heat treated. Drying can becarried by any conventional method in the art. Examples suitable fordrying kaolin include spray drying, flash drying, rotary drying, orother conglomeration techniques.

The dried kaolin is typically pulverized prior to the heat treatment.Pulverization may be conducted in any suitable manner. In oneembodiment, the kaolin is pulverized at least once. In anotherembodiment, the kaolin is pulverized in at least two separate acts(twice pulverized). The pulverization may break up any agglomerates thatmay be present. Such agglomerates may form during drying, changing theparticle size achieved by high-speed centrifugation and other methodsteps.

When kaolin is heated, it undergoes a series of characteristic changes,detectable by various methods including differential thermal analysis(DTA). Heat treatment may be employed to form one or more of metakaolin,partially calcined kaolin, and fully calcined kaolin, depending on thetemperature/duration of the heat treatment. In an embodiment, the heattreatment employed results in fully calcined kaolin. As used herein,“fully calcined kaolin” refers to kaolin that has been heat treated at atemperature from 900° C. to about 1200° C. In an embodiment, the heattreatment employed results in metakaolin.

Heat treatment is performed under one of an inert atmosphere, anoxidizing atmosphere, and a reducing atmosphere. Calcining destroys thecrystallinity of hydrous kaolin and renders the kaolin substantiallyamorphous. Calcination occurs after heating at temperatures in the rangefrom about 700 to about 1200° C. for a sufficient period of time.Commercial vertical and horizontal rotary calciners can be used toproduce metakaolin, partially calcined kaolin, and/or calcined kaolin.Operation is controlled to avoid calcining at sufficiently hightemperatures to form unwanted mullite (3Al₂O₃.SiO₂).

The heat treated kaolin may be subject to addition wet centrifugation orair classification steps, to produce an even finer size distributionproduction. For instance, a fully calcined kaolin may be slurried at 20wt. % in water, and subjected to centrifugation to produce an even finersize fraction.

In some methods in the prior art, a delamination step is carried outduring the refining of kaolin, for instance after classification.Delamination processes include ball milling, media grinding (includingstirred media grinding and/or high energy media grinding). In anembodiment of the present method, the method excludes any delaminationprocess.

In certain embodiments, the method for preparing the heat-treated kaolinproduct can include providing a first kaolin feedstream having at leastabout 88-89% by weight of the particles having size of 1 μm or less;classifying the first kaolin feedstream by centrifugation to provide afine particle size distribution of at least about 97-98% by weight ofthe particles having size of 1 μm or less; filtering the first kaolinfeedstream to produce a filter cake; dispersing the filtrate in asodium-free dispersion agent to provide a second kaolin feedstream; anddrying and heat treating the second kaolin feedstream, wherein themethod for preparing the heat-treated kaolin does not include ableaching step. The method can provide a heat-treated kaolin product asdescribed herein.

The improved optical (gloss and light scattering) properties with finerand narrow particle size distribution of the kaolin of the disclosureshould be highly advantageous for applications such as thermal paper,industrial and architectural coatings, and the like. For architecturalor industrial coatings, calcined kaolin pigment should improve coverage,and optical properties, thus resulting in use of less calcined pigmentas compared to the prior art or reduction of TiO₂ for achieving similaroptical properties.

In an embodiment, the kaolin disclosed herein is used in thermal paper.In thermal paper applications when used as the base coating, theinventive pigments should improve the insulation capacity, coverage,smoothness and wax absorption of the pre-coating used in direct thermalpaper. Thermal paper typically has at least three layers: a substratelayer, an active layer for forming an image, and a base layer betweenthe substrate layer and active layer. The base layer contains a binderand a calcined kaolin as a porosity improver, and may further andoptionally contain a dispersant, wetting agent, and other additives. Theporosity improver contributes to the desirable thermal effusivityproperties of the base layer. The base layer contains a sufficientamount of a porosity improver to contribute to providing insulatingproperties, such as a beneficial thermal effusivity, that facilitatehigh quality image formation in the active layer. In one embodiment, thebase layer contains about 5% by weight or more and about 95% by weightor less of a porosity improver. In another embodiment, the base layercontains about 15% by weight or more and about 90% by weight or less ofa porosity improver. In yet another embodiment, the base layer containsabout 15% by weight or more and about 40% by weight or less of aporosity improver. See, e.g., U.S. Pat. No. 7,902,117.

In addition, the calcined kaolin material can be used in paper, and inparticular, pigment for thermal paper base coating, coatings, wire andcable, plastics, tire and rubber, construction. Exemplary monomers foruse in preparing paper coating or binding formulations comprisingcalcined kaolin are disclosed in U.S. Pat. No. 8,642,182.

Additionally, due to the lower abrasion and other physical properties,the calcined kaolin of the disclosure can also be used in paper coatingand filling.

The calcined kaolin of the disclosure can also be surface treated usingsilanes for wire and cable and other engineered plastics applications.

In an embodiment, the heat-treated kaolin of the disclosure can be usedin an industrial or architectural coating. The kaolin of the disclosureprovides a higher contrast ratio which indicates improved higher power,improved whiteness and brightness, and/or higher tinting strength insuch a coating, compared to commercial kaolins currently available.

Accordingly, the kaolin disclosed herein can be used for a variety ofapplications. Non-limiting uses for the calcined kaolin disclosed hereininclude the manufacture of paper and paperboard products, papercoatings, ceramic products, paints, polymers, rubbers, engineeredplastics, and inks. The kaolin process described herein can also be usedto process any type of crude kaolin clay: soft and hard, differentcolors (grey, white, cream, yellow, brown, red, and pink), and mixturesthereof.

EXAMPLES

The products, compositions and methods of making and using are furtherdescribed in detail by reference to the following experimental examples.These examples are provided for purposes of illustration only, and arenot intended to be limiting unless otherwise specified. Thus, theproducts, compositions and methods of the disclosure should in no way beconstrued as being limited to the following examples, but rather, shouldbe construed to encompass any and all variations which become evident asa result of the teaching provided herein.

Properties described in the following examples were assessed by thefollowing methods.

Particle size distribution (PSD) was measured by sedimentation of theparticle material in a fully dispersed condition in a standard aqueousmedium, such as water, using a SEDIGRAPH 5100 particle size analyzer(Micromeretics Corporation). The data are reported as equivalentspherical diameters (e.s.d.) on a weight percentage basis. The meanparticle size d₅₀ is the value determined in this way of the particlee.s.d. at which there are 50% by weight of the particles that have ane.s.d. less than the d₅₀ value.

Brightness was determined by the TAPPI standard method T452. The dataare reported as the percentage reflectance to light of a 457 nmwavelength (GEB value).

Einlehner abrasion loss was determined by an Einlehner AT 1000 Abrasiontester, using 15% by weight solids and 100,000 revolutions. TheEinlehner abrasion is reported in mg loss/100,000 revolutions (mgloss/10⁵ rev).

Oil absorption was determined using ASTM D 281 “Oil Absorption bySpatula Rub-out.” The data are reported in pounds of oil absorbed per100 pounds of calcined kaolin (%).

Surface area was determined by the art-recognized BET method using N₂ asthe adsorbate.

Examples 1 and 2 were prepared from exclusively grey kaolin crude of thetertiary crude type.

Example 1

This example provides data for a calcined kaolin prepared according tothe present disclosure and a comparative commercially available calcinedkaolin. The commercially available calcined kaolin (also referred toherein as “control kaolin”) is produced from a chemically dispersedblunged/degritted hydrous kaolin crude feedstock that is subject to aclassification step and a beneficiation step to produce a feedstream forcalcination. The control kaolin feedstream has 88-89%<1 micron particlesize, as measured by SEDIGRAPH 5100 particle size analyzer(Micromeritics Corporation, USA). The comparative calcined kaolin inthis example, Comparative Sample 1 was prepared by obtaining a sample ofthe control kaolin feedstream, and spray drying it in the laboratory.The dried material was then pulverized using a Micro pulverizer equippedwith a 0.020″ screen and then calcined in a laboratory muffle furnace at1,079° C. (i.e., 1,975° F.) for a 60 minute soak time. The resultingcalcined kaolin product was then pulverized using the Micro pulverizerequipped with 0.020″ screen.

Sample 1 is an embodiment of the inventive calcined kaolin. Sample 1 wasmade by diluting kaolin from the control kaolin feedstream to about 30%solids, followed by centrifugation to obtain a fines fraction with97-98%<1 micron particle size. Fines fractions obtained fromcentrifugation step were then subjected to flocculation (“flocked”)using 8 lbs/ton of alum and sulfuric acid at pH=3.5, followed by labvacuum filtration to dewater and remove soluble salts. The resultingfilter cake contained about 55% solids. The filter cake was thenre-dispersed with ammonium hydroxide at pH about 10.0. The dispersedfilter slip was then spray dried, pulverized and calcined in alaboratory muffle furnace at 1,079° C. (i.e., 1,975° F.) for 60 minutessoak time, as described for Comparative Sample 1. The resulting calcinedkaolin was then pulverized using the Micro pulverizer, as described forComparative Sample 1.

Physical and optical properties of Comparative Sample 1 and Sample 1were measured. Table 7 below shows the properties of Comparative Sample1 (commercially available calcined kaolin), and Sample 1 (the inventivecalcined kaolin).

TABLE 7 Comparative Sample 1 Sample 1 Commercially available Inventivecalcined kaolin Calcined Kaolin G.E. Brightness, % 92.3 93.9 EinlehnerAbrasion 18.1 13.2 loss in mg/10⁵ rev Oil Absorption, % 89 110 SurfaceArea (m²/g) 16.9 19.9 +325 mesh Residue, % 0.0095 0.0016 PSD  % ≦10 μm96 100   % ≦5 μm 92 96   % ≦2 μm 82 91   % ≦1 μm 65 86 % ≦0.5 μm 19 37 %≦0.3 μm 6 7 % ≦0.2 μm 3 5 Median Particle Size, μm 0.77 0.57

As shown in Table 7, Sample 1 has significantly higher GE brightness andlower Einlehner abrasion value than the Comparative Sample 1. Further,Sample 1 has a much finer and narrower particle size distribution bothat the coarse end (>5 microns) and the fine end (<2 microns) ofdistribution, as well as a finer median particle size, compared to theComparative Sample 1. In addition, oil absorption value for Sample 1 ismarkedly increased, which is a desirable property for certainapplications such as architectural and industrial coatings and thermalpaper applications (wax absorption etc.). The inventive calcined kaolinproduct had a lower +325 mesh residue content of 0.0016% (16 ppm)compared to 0.0095% (95 ppm) for the Comparative Sample 1. The data alsoshow that surface area of Sample 1 is increased from 16.9 m²/g forComparative Sample 1 to 19.9 m²/g for the inventive calcined kaolin.This is another indication of finer particle size distribution ofinventive calcined kaolin product. Thus, the additional processing stepsused to prepare Sample 1 advantageously result in a calcined kaolin thathas improved optical properties, improved oil absorption, improvedsurface area, and reduced abrasion, compared to Comparative Sample 1.

Example 2

In this example, another calcined kaolin prepared according to thepresent disclosure was prepared and compared to Comparative Sample 1(regular ANSILEX® 93). The inventive calcined kaolin embodiment, Sample2, was prepared without additional centrifugation step used to prepareSample 1. Sample 2 was prepared by diluting kaolin from the regularANSILEX® 93 feed to about 25% solids, followed by flocculation using 8lbs/ton of alum and sulfuric acid at pH=3.5 followed. The resultingflocked clay was then subjected to filtration using the lab vacuumfiltration system to dewater and remove soluble salts. The resultingfilter cake contained about 55% solids. The filter cake was thenre-dispersed with ammonium hydroxide at pH about 10.0. The dispersedfilter slip was then spray dried, pulverized and calcined in alaboratory muffle furnace at 1,079° C. (i.e., 1,975° F.) for 60 minutessoak time, as described in Example 2. The resulting calcined kaolin wasthen pulverized using the lab Micro pulverizer, and physical and opticalproperties of Sample 2 were measured. The data are presented in Table 8.

TABLE 8 Comparative Sample 1 Sample 2 Commercially available Inventivecalcined kaolin Calcined Kaolin G.E. Brightness, % 92.3 92.4 EinlehnerAbrasion 18.1 nd loss in mg/10⁵ rev Oil Absorption, % 89 109 SurfaceArea (m²/g) 16.9 17.8 +325 mesh Residue, % 0.0095 0.0072 PSD  % ≦10 μm96 100   % ≦5 μm 92 97   % ≦2 μm 82 90   % ≦1 μm 65 77 % ≦0.5 μm 19 29 %≦0.3 μm 6 4 % ≦0.2 μm 3 0 Median Particle Size, μm 0.77 0.63 “nd” = notdetermined

As shown in Table 8, the brightness of Sample 2 is similar toComparative Sample 1. However, Sample 2 (the inventive calcined kaolin)has a finer and narrower particle size distribution both at the coarseend (>5 microns) and the fine end (<2 microns) of distribution, as wellas a finer median particle size in comparison to Comparative Sample 1.The data also show that surface area of the inventive calcined kaolin isincreased slightly from 16.9 m²/g for regular ANSILEX® 93 to 17.8 m²/gfor inventive calcined kaolin. The inventive calcined kaolin product hada lower +325 mesh residue content of 0.0072% (72 ppm) compared to0.0095% (95 ppm) for the Comparative Sample 1. There is also an increasein oil absorption value for the inventive kaolin as compared toComparative Sample 1.

The results presented in Examples 1 and 2 (Table 7 and Table 8)demonstrate the significance of an additional centrifugation step forobtaining a finer calciner feedstream that results in the calcinedkaolin product with much finer and narrower particle size distribution,as well as other improved properties (e.g., higher GE brightness, lowerEinlehner abrasion, higher surface area, higher oil absorption),compared to Comparative Sample 1. The data in Examples 1 and 2 alsoclearly illustrate the additional benefits of filtration combined withusing an ammonia-based filter dispersant that results in a finer andnarrower particle size distribution inventive calcined product as well.Thus, the additional processing steps used to prepare inventive Samples1 and 2 advantageously result in a calcined kaolin that has both a finerand a narrower particle size distribution as compared to the prior art.

Example 3

The inventive calcined kaolin embodiment, Sample 3, in this example wasproduced from an ultra-fine hydrous kaolin feedstream, obtained fromBASF's kaolin manufacturing operations. The kaolin in this feedstreamcontains about 50% grey crudes, the balance being the other types ofcrudes including white, cream, brown, reddish, pink colored crudes. Theultra-fine hydrous kaolin feedstream is prepared from a chemicallydispersed hydrous kaolin crude feedstock subjected to coarse sizeclassification, flotation, ozonation, and ultra-fine size classificationsteps at BASF's manufacturing operations. A disc-nozzle centrifuge(Alpha Laval) is utilized to obtain the ultra-fine size with at least70% by weight of the particles less than 0.3 microns.

In this example, the fines fraction from the plant AlphaLaval centrifugewith 73%<0.3 microns particle size was flocked, filtered andre-dispersed using ammonia as the dispersant at pH about 10.0, asdescribed in Example 1. The re-dispersed filter product was then spraydried followed by pulverization with a Micro pulverizer. The preparedfeed material was then calcined in a lab muffle furnace at 1,079° C.(1975° F.) temperature for 60 min soak time. The resulting calcinedproduct was then pulverized using a Micro pulverizer, and physical andoptical properties of Sample 3 were measured.

Comparative 2 was prepared in the same way as Sample 3, except that thefilter cake was re-dispersed using a sodium based dispersant (instead ofusing ammonia). Specifically, a blend of sodium polyacrylate/sodaash/sodium hexametaphosphate (SAP) was used for re-dispersing filterproduct at pH about 7. The other process parameters such as spraydrying, pulverizing and calcining were kept the same. The particle sizedistribution of Comparative Sample 2 was measured.

The data are presented in Table 9.

TABLE 9 Sample 3 Inventive Calcined Kaolin Comparative Comparative(Ammonia Sample 2 Sample 1 Dispersed) (SAP Dispersed) G.E. Brightness, %92.3 94.3 nd Einlehner Abrasion 18.1 10.1 nd loss in mg/10⁵ rev OilAbsorption, % 89 113 nd Surface Area (m²/g) 16.9 20.8 nd +325 meshResidue, % 0.0095 0.0051 nd PSD  % ≦10 μm 96 99 94   % ≦5 μm 92 94 84  % ≦2 μm 82 89 73   % ≦1 μm 65 82 63 % ≦0.5 μm 19 33 22 % ≦0.3 μm 6 174 % ≦0.2 μm 3 7 1 Median Particle Size, μm 0.77 0.59 0.75 “nd” = notdetermined

As shown in Table 9, the inventive calcined kaolin which is dispersedusing ammonia at the filter step has a finer and narrower particle sizedistribution both at the coarse end (>5 microns) and the fine end (<2microns) of distribution, as well as finer median particle size,compared to Comparative Sample 1. In contrast, Comparative Sample 2 (thefilter product dispersed using sodium based dispersants) results in amuch coarser particle size calcined product. From this example, one canappreciate the advantages of using ammonia as the secondary dispersantat the filtration step for obtaining finer and narrow particle sizeinventive calcined product.

Sample 3 (the inventive calcined kaolin) has significantly higher GEbrightness and lower Einlehner abrasion value compared to ComparativeSample 1. The inventive calcined kaolin product had a lower +325 meshresidue content of 0.0051% (51 ppm) compared to 0.0095% (95 ppm) for theComparative Sample 1. In addition, surface area of the inventivecalcined kaolin is increased remarkably from 16.9 m²/g for ComparativeSample 1 to 20.8 m²/g for inventive calcined kaolin. There is alsosignificant increase in oil absorption value for inventive kaolincompared to Comparative Sample 1.

The particle size distributions for Samples 1-3 (embodiments of theinventive calcined kaolin) and Comparative Sample 1 (commerciallyavailable calcined kaolin) is depicted graphically in FIG. 4. The curvesfor the particle distribution of Samples 1-3 are steeper than the curvefor the comparative sample, indicative of the narrower particle sizedistribution for Samples 1-3, compared to Comparative Sample 1.

Example 4

Light scattering data for Comparative Sample 1 and Samples 1-3 (theinventive calcined kaolin) are shown in Table 10. Light scattering wasdetermined by applying a film of pigment onto optically smooth blackglass from a 30% solids (by weight) mixture of pigment and water using a0.25 mil Bird Bar. The reflectance values of the pigment films after airdrying are measured at wavelengths of 457 nm and 577 nm by means of areflectance meter having an integrated sphere geometry like an Elrephoreflectometer. The reflectance values are converted by the use ofKubelka-Munk equations to light scattering coefficients (m²/g). Similarto light scattering, gloss is determined by applying a film of pigmentonto optically smooth black glass from a 30% solids (by weight) mixtureof pigment and water using a 0.25 mil Bird Bar. Gloss is measured usinga Technidyne T480 gloss meter (Technidyne Corporation, New Albany, Ind.)at 75 degrees (PL Method 50C).

TABLE 10 Sample 1 Sample 2 Sample 3 Inventive Inventive InventiveComparative Calcined Calcined Calcined Sample 1 Product Product ProductGloss, % 31.3 43.3 36.6 31.0 S₄₅₇ (m²/g) 0.271 0.331 0.309 0.327 S₅₇₇(m²/g) 0.214 0.229 0.225 0.227

The data in Table 10 demonstrate that the method of the disclosureproduces calcined kaolin with improved light scattering properties atboth wavelength 457 nm and wavelength 577 nm. Additionally, there issignificant gloss improvement for the inventive calcined kaolin productscompared to Comparative Sample 1. Sample 1 exhibits a particularly largeimprovement in gloss, having a gloss that is over 30% larger than thatof Comparative Sample 1. The improved light scattering and glossproperties are an indication of similar or better morphology for theinventive calcined product as compared to Comparative Sample 1.

Example 5

Chemical composition for Comparative Sample 1 and the inventive calcinedkaolin Samples 1-3 was obtained by determination of the bulk elementalcomposition using a Panalytical X-Ray Fluorescence Spectroscopy (XRF).In this analytical measurement procedure with the XRF machine, prior toplacing the samples to the XRF carousel, each sample is first dried inan oven to ensure the surface moisture is removed, followed by firingsamples in a muffle furnace at 1,000° C. for 60 minutes to determineloss-on-ignition (LOI) value. After this step, the sample is cooled downin a desiccator and pressed into a pellet using cellulose as the binder(note that cellulose is inert for XRF analysis performed on kaolinsamples).

Table 11 contains XRF data for the three inventive calcined products aswell as Comparative Sample 1. The XRF produces a list of the percentagesof nine chemical elements (Si, Al, Na, K, Ti, Fe, Ca, Mg and P)expressed as oxides: Sift, Al₂O₃, Na₂O, K₂O, TiO₂, Fe₂O₃, CaO, MgO, andP₂O₅. The results are reported on volatile free basis. Also presented inthe table are the LOI values for each product.

TABLE 11 Sample 2 Sample 3 Sample 1 Inventive Inventive ComparativeInventive Calcined Calcined Sample 1 Calcined Product Product Product %SiO₂ 53.5 53.3 53.8 54.6 % Al₂O₃ 45.9 45.6 45.8 46.6 % Na₂O 0.32 0.080.08 0.09 % K₂O 0.18 0.18 0.22 0.16 % TiO₂ 1.67 1.45 1.73 0.52 % Fe₂O₃0.92 0.93 0.96 0.94 % CaO 0.11 0.09 0.08 0.02 % MgO 0.04 0.05 0.05 0.06% P₂O₅ 0.11 0.08 0.09 0.07 Total 102.8 101.8 102.8 103.0 % LOI 0.30 0.350.29 0.30

As can be seen from the data in Table 11, Samples 1 through 3 containonly about a quarter of the sodium contained by Comparative Sample 1.Thus, the processing steps used to prepare Samples 1 through 3advantageously result in a large reduction in sodium content.

It is believed, without being held to theory, that sodium, for instancefrom a sodium dispersant used in preparing a chemically dispersedblunged/degritted hydrous kaolin crude feedstock, fills pores in thekaolin particles during calcination thus reducing surface area and porevolume of final calcined product. The reduction in sodium content istherefore believed to contribute to the improved oil absorption andsurface area properties of the kaolin prepared according to the methodof this disclosure.

In addition, the amount of discolored titania (anatase) impurity isreduced to a great degree from about 1.7% for Comparative Sample 1 to1.45% for Sample 1 due to the additional centrifugation step applied toremove coarser and denser particles, including discolored titaniaimpurities. Sample 3 also has a reduced amount of TiO₂, indicating thatthe method used to prepare Sample 3 reduces titanium contamination inthe kaolin feedstream.

Therefore, the processing steps used to prepare Sample 1 and 3advantageously result in a favorable reduction in titania content, whichin turn results in better calcination response and higher brightnessproduct (see Sample 1 in Table 7 and Sample 3 in Table 9).

Chemical composition was also determined for the kaolin samplesdispersed using ammonia (Sample 3) or sodium-based dispersant(Comparative Sample 2), described in Example 3. Sample 3 and ComparativeSample 2 are prepared identically except for the dispersants used duringthe filtration step prior to calcination. The data are presented inTable 12.

TABLE 12 Comparative Sample 2 Not Inventive Calcined Sample 3 KaolinInventive Calcined Dispersant Used at Filter Sodium Based Kaolin Step(SAP) Ammonia % SiO₂ 53.9 54.6 % Al₂O₃ 45.8 46.6 % Na₂O 0.46 0.09 % K₂O0.16 0.16 % TiO₂ 0.53 0.52 % Fe₂O₃ 0.93 0.94 % CaO 0.02 0.02 % MgO 0.060.06 % P₂O₅ 0.22 0.07 Total 102.1 103.0 % LOI 0.32 0.30

Chemical composition was also determined for the kaolin samplesdispersed using ammonia (Sample 3) or sodium-based dispersant(Comparative Sample 2), described in Example 3. Sample 3 and ComparativeSample 2 are prepared identically except for the dispersants used duringthe filtration step prior to calcination. The data are presented inTable 12.

The data for Sample 3 and Comparative Sample 2, as presented in Table12, illustrate that use of an ammonia-based dispersant significantlyreduces sodium content of the final calcined product, compared tocalcined kaolin products prepared using an sodium-based dispersant. Forinstance, Sample 3 contains only about 20% of the sodium present inComparative Sample 2 in which the calciner feed was dispersed using asodium-based dispersant. It is also notable that there is about 32%reduction in P₂O₅ value for the inventive kaolin product as well. Thisresult suggests that the phosphate (likely as a result of using sodiumhexa metaphosphate in sodium based dispersant) is also removed from thekaolin surface during the filtration step (removed with the filtrate).The presence of excessive amount of alkalis, such as sodium, in calcinerfeed materials can lead to fluxing during calcination, which causesaggregation of particles. Therefore, any reduction in sodium obtained bythe method of the disclosure, as illustrated in Examples 1, 2 and 3, isalso believed to reduce the incidence and/or the extent of fluxingduring calcination, and thereby contribute to the improved narrowparticle size distribution and improve morphology of the final calcinedkaolin product obtained by the method of the disclosure.

Example 6

A paint was prepared comprising either a commercially available finecalcined kaolin (Comparative Sample 4) or a calcined kaolin of thisdisclosure (Sample 4). The paint formulation is shown in Table 13.

TABLE 13 75 PVC Formula Component Parts Water 253.8 Cellulosic Thickener4.9 Dispersing Agent 2.0 Wetting Agent 2.0 Defoamer 2.5 Biocide 3.0Propylene Glycol 20.0 General Purpose TiO₂ 100.0 CaCO₃, 5 micron 280.0Kaolin 75.0 Water 40.3 Buffer 1.8 Defoamer 1.0 Coalescent 7.0 Vinylacrylic emulsion 200.0 Total 993.30

The properties of the two paint formulations were characterized by:viscosity, contrast ratio, brightness, whiteness, yellowness, Hunter L,a, and b values, gloss at 20 degrees and at 60 degrees, sheen at 85degrees, and tint strength.

Viscosity is a measure of resistance to flow. Viscosity was measuredusing a Stormer viscometer and is expressed as Krebs Units (KU).

Contrast ratio was determined by measuring reflectance over a blacksubstrate and over a white substrate using a Hunter Spectrophotometer.The contrast ratio is the ratio of reflectance of black/reflectance ofwhite. Whiteness, Yellowness, and Hunter L, a, b values were measuredusing a Hunter Spectrophotometer.

Gloss and sheen were measured using a gloss meter at three angles ofincidence (20, 60 and 85).

Tinting Strength was assessed using a white base containing the kaolinthat was tinted (black colorant added) and reflectance of thecorresponding gray was measured. Comparative Sample 4 was measuredagainst Sample 4 and the lightness of the gray shade is given anumerical value based on the reflectance. The higher the tintingstrength, the lighter is the shade.

The data are shown in Table 14.

TABLE 14 Property Comparative Sample 4 Sample 4 Viscosity, KU 103 105Contrast Ratio 3 mils 95.1 96.1 Brightness 87.43 88.12 Whiteness 79.7780.50 Yellowness 2.64 2.60 Hunter L 95.83 96.11 Hunter a −0.62 −0.61Hunter b 2.08 2.05 Gloss @ 20 degrees 1.4 1.4 Gloss @ 60 degrees 2.4 2.8Sheen @ 85 degrees 4.3 8.8 Tint Strength 100.0 115.5

These data show improved hiding power (higher contrast ratio), improvedwhiteness and brightness and much higher tinting strength for Sample 4,containing a calcined kaolin of this disclosure, compared to ComparativeSample 4. Higher tinting strength advantageously allows reduction ofTiO₂ thereby reducing overall formulation costs.

The disclosures of each and every patent, patent application, andpublication cited herein are hereby incorporated herein by reference intheir entirety for all purposes.

While the products, compositions, methods of making them, and theirmethods of use have been disclosed with reference to specificembodiments, it is apparent that other embodiments and variations may bedevised by others skilled in the art without departing from the truespirit and scope of the described products and methods. The appendedclaims are intended to be construed to include all such embodiments andequivalent variations.

The compositions and methods of the appended claims are not limited inscope by the specific compositions and methods described herein, whichare intended as illustrations of a few aspects of the claims and anycompositions and methods that are functionally equivalent are intendedto fall within the scope of the claims. Various modifications of thecompositions and methods in addition to those shown and described hereinare intended to fall within the scope of the appended claims. Further,while only certain representative materials and method steps disclosedherein are specifically described, other combinations of the materialsand method steps also are intended to fall within the scope of theappended claims, even if not specifically recited. Thus, a combinationof steps, elements, components, or constituents may be explicitlymentioned herein; however, other combinations of steps, elements,components, and constituents are included, even though not explicitlystated.

The term “comprising” and variations thereof as used herein is usedsynonymously with the term “including” and variations thereof and areopen, non-limiting terms. Although the terms “comprising” and“including” have been used herein to describe various embodiments, theterms “consisting essentially of” and “consisting of” can be used inplace of “comprising” and “including” to provide for more specificembodiments and are also disclosed. As used in this disclosure and inthe appended claims, the singular forms “a”, “an”, “the”, include pluralreferents unless the context clearly dictates otherwise. The disclosureof percentage ranges and other ranges herein includes the disclosure ofthe endpoints of the range and any integers provided in the range.

What is claimed is:
 1. A heat-treated kaolin having a GE brightness ofat least about 92 and a particle size distribution of: equal to orgreater than 99% by weight of particles with an equivalent sphericaldiameter (e.s.d.) of less than 10 microns; equal to or greater than 93%by weight of particles with an e.s.d. of less than 5 microns; equal toor greater than 85% by weight of particles with an e.s.d. of less than 2microns; equal to or greater than 77% by weight of particles with ane.s.d. of less than 1 microns; and equal to or greater than 25% byweight of particles with an e.s.d. of less than 0.5 micron, wherein theheat treated kaolin has a +325 mesh residue content of 300 ppm or less.2. A heat-treated kaolin having a GE brightness of at least about 92 anda particle size distribution of: equal to or greater than 99% by weightof particles with an equivalent spherical diameter (e.s.d.) of less than10 microns; equal to or greater than 93% by weight of particles with ane.s.d. of less than 5 microns; equal to or greater than 85% by weight ofparticles with an e.s.d. of less than 2 microns; equal to or greaterthan 77% by weight of particles with an e.s.d. of less than 1 microns;and equal to or greater than 25% by weight of particles with an e.s.d.of less than 0.5 micron, wherein the heat-treated kaolin has a sodiumoxide content of less than or equal to 0.25% by weight of theheat-treated kaolin.
 3. The heat-treated kaolin according to claim 2,having a +325 mesh residue content of 300 ppm or less.
 4. Theheat-treated kaolin according to claim 1 having a particle sizedistribution of: 99% to 100% by weight of particles with an e.s.d. ofless than 10 microns; 93% to 100% by weight of particles with an e.s.d.of less than 5 microns; 85% to 98% by weight of particles with an e.s.d.of less than 2 microns; 77% to 92% by weight of particles with an e.s.d.of less than 1 microns; and 25% to 46% by weight of particles with ane.s.d. of less than 0.5 micron.
 5. The heat-treated kaolin according toclaim 1, having a +325 mesh residue content of 90 ppm or less.
 6. Theheat-treated kaolin according to claim 1, having a sodium oxide contentless than or equal to 0.1% by weight of the heat-treated kaolin.
 7. Theheat-treated kaolin according to claim 1, having a GE brightness of atleast about 92 to about
 96. 8. The heat-treated kaolin according toclaim 1, having a median particle size (d50) of 0.50 to 0.59 micron. 9.The heat-treated kaolin according to claim 1, having an oil absorptionof greater than 100 to 140 lbs oil/100 lbs heat-treated kaolin.
 10. Theheat-treated kaolin according to claim 1, having a scatteringcoefficient at 457 nanometers of about 0.305 to about 0.335 m²/g. 11.The heat-treated kaolin according to claim 1, having a scatteringcoefficient at 577 nanometers of about 0.223 to about 0.230 m²/g. 12.The heat-treated kaolin according to claim 1, having a surface area ofabout 17.0 to about 25.0 m²/g.
 13. The heat-treated kaolin according toclaim 1 having an Einlehner abrasion loss of 9 to 18 mg/10⁵ rev.
 14. Theheat-treated kaolin according to claim 1 having a gloss of about 30% toabout 45%.
 15. The heat-treated kaolin according to claim 2, having a GEbrightness of at least about 92 to about
 96. 16. The heat-treated kaolinaccording to claim 2, having a median particle size (d50) of 0.50 to0.59 micron.
 17. The heat-treated kaolin according to claim 2, having asurface area of about 17.0 to about 25.0 m²/g.
 18. The heat-treatedkaolin according to claim 2 having an Einlehner abrasion loss of 9 to 18mg/10⁵ rev.
 19. The heat-treated kaolin according to claim 2 having agloss of about 30% to about 45%.
 20. A method for preparing theheat-treated kaolin product, comprising the steps of: providing a firstkaolin feedstream having at least about 88-89% by weight of theparticles having size of 1 μm or less; classifying the first kaolinfeedstream by centrifugation to provide a fine particle sizedistribution of at least about 97-98% by weight of the particles havingsize of 1 μm or less; filtering the first kaolin feedstream to produce afilter cake; dispersing the filtrate in a sodium-free dispersion agentto provide a second kaolin feedstream; and drying and heat treating thesecond kaolin feedstream, wherein the method for preparing theheat-treated kaolin does not include a reductive bleaching step.
 21. Themethod according to claim 20, further comprising flocculating the firstfeedstream prior to the filtering step.
 22. The method according toclaim 20, wherein the sodium-free dispersion agent is an ammonia-baseddispersion agent.
 23. The method according to claim 20, wherein thesecond kaolin feedstream has a pH of about
 10. 24. The method accordingto claim 20, wherein heat treating comprises calcining at a temperatureof from about 900° C. to about 1200° C. to produce a fully calcinedkaolin.
 25. The method according to claim 20, wherein the providing stepcomprises processing a blunged/degritted hydrous kaolin crude feedstockby one or more of magnetic separation, flotation, ozonation, orselective flocculation to produce the first kaolin feedstream having atleast about 88-89% by weight of the particles having size of 1 μm orless.
 26. The method according to claim 20, wherein the method excludesdelamination processes.
 27. The method according to claim 20, whereinthe classifying step, filtering step, dispersing step, and drying andcalcining step exclude a sodium-based dispersion agent.